1. Field of the Invention
The present invention relates to an optical scanner used in a laser printer, a laser facsimile, a digital copying machine, etc.
2. Description of the Related Art
There are many various kinds of proposed optical scanners in which light from a light source is deflected and scanned by various kinds of deflectors such as a rotary polygon mirror and a pyramidal mirror to scan a scanning face of a scanned medium such as a photosensitive body, etc. These optical scanners are used in optical scanning sections of a laser printer, a laser facsimile, a digital copying machine, etc.
In a deflector such as the rotary polygon mirror used in the optical scanners, field curvature is caused when an angle of deflection of light is set to be large at the times of deflecting and scanning operations. It is necessary to use an optical system such as an f .theta. lens so as to correct this field curvature. Otherwise, it is necessary to dispose a correcting means for mechanically moving a lens of the optical system arranged before the deflector, etc. Accordingly, the optical scanners are large-sized and are increased in cost. In a deflector using the pyramidal mirror, there is a disadvantage that the pitch of a light beam is changed in a normal using method of the pyramidal mirror so that it is not easy to use multiple light beams.